ML14143A253

Watts Bar, Unit 2, Response to Audit for the Fuel Rod Design Effects of Thermal Conductivity Degradation

ML14143A253
Person / Time
Site:	Watts Bar
Issue date:	05/22/2014
From:	Kersting P J Westinghouse
To:	Office of Nuclear Reactor Regulation
References
CN-WATTS-122, Rev. 0
Download: ML14143A253 (26)

Text

ENCLOSURE 3 Tennessee Valley Authority Watts Bar Nuclear Plant, Unit 2 Docket No. 50-391 NON-PROPRIETARY ATTACHMENT TO WESTINGHOUSE LETTER TO TVA WBT-D-4833, DATED MAY 16, 2014, "TDC NRC AUDIT" E3-1 Westinghouse Non-Proprietary Class 3 CE- 14-3 71, Attachment 2 CE-14-371, Attachment 2 Response to Watts Bar Unit 2 NRC Audit for the Fuel Rod Design Effects of Thermal Conductivity Degradation, Non-Proprietary 02014 Westinghouse Electric Company LLC. All rights reserved.Core Engineering Memo Template Version 1-0 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 1 0 A-i Westinghouse Response to NRC Request for Additional Information for Audit of Westinghouse Evaluation of Fuel Thermal Conductivity Degradation for Watts Bar Unit 2 Fuel Authored: Paul J. Kersting PWR Core Methods, Methods & Technology Verified: Tim M. Crede Fuel Rod and Thermal Hydraulic Design, Core Engineering Approved: Keith J. Drudy PWR Core Methods, Methods & Technology

Attachment:

24 pages@2014 Westinghouse Electric Company LLC All Rights Reserved O Westinghouse Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 1 o A-2 Provided in this Attachment are the Westinghouse responses to the Nuclear Regulatory Commission (NRC) Requests for Additional Information (RAI) regarding the Watts Bar Unit 2 fuel rod design with fuel thermal conductivity degradation with burnup (TCD) effects in Reference

1. The NRC request is repeated for each item, followed by the Westinghouse response.1. The NRC staff intends to run FRAPCON-3.4 benchmark calculations of the fuel rod design. Provide the following inputs for FRAPCON 3.4.A. Rod Power History, KWlft as a function of GWdlMTU 1. Bounding thermal-mechanical operating envelope for both fuel types (i.e., U0 2 and IFBA)Response: It is understood that the NRC intends to perform audit analyses using the FRAPCON 3.4 fuel performance code for the design parameters significantly impacted by TCD: rod internal pressure, transient clad strain and power to fuel centerline melt. For the rod internal pressure analysis and the power to melt analysis, Westinghouse uses a a1". Table 1 provides this [ ]ac for a limiting rod internal pressure analysis.

In order to assess TCD impacts over the full burnup capability of the fuel, an additional cycle of operation was added to the design power history to obtain end of life rod burnup of [ ]ac This power history, illustrated in Figure 1,]a,C, For the transient clad strain analysis, Westinghouse

]ac. The power history for the limiting transient clad strain analysis is given in Table 2 and Figure 2. The limiting strain results occurred [a,c, Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 1 0 A-3 a,c Table I Bounding Rod Power History for Limiting Rod Internal Pressure Analysis Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 1 0 A-4 Table 2 Rod Power History for Limiting Transient Clad Strain Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 1 0 A-5 Figure 1 Bounding Rod Power History for Limiting Rod Internal Pressure Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-6 Figure 2 Rod Power History for Limiting Transient Clad Strain Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-7 2. Discuss any application of rod power uncertainties Response: The effects of uncertainties in the steady-state rod power history]a,c.In the calculation of the power to fuel melt limit, the fuel temperature is calculated as a function of both power and burnup. Uncertainties on the actual transient power capability are applied on an event-specific basis outside of the fuel rod design analysis.For the transient clad strain analysis, uncertainties are a,C 3. Include power histories for different pellet designs for both fuel types Response: Reference limiting case power histories are provided in response to Item 1 .A.1 above.Ia,c.B. Axial Power Distribution (Fz at each axial node)1. Include AXPDs for different axial blanket configurations.

Response: The power history provided for the rod internal pressure case in Table 1 has 34 burnup steps. The axial power shapes corresponding to each burnup step for the rod internal pressure limiting rod case are given in Table 3. The rod internal pressure analysis I]ac but since FRAPCON 3.4 is limited to a maximum of 17 axial nodes, the axial power shapes provided in Table 3 are defined for 17 equal axial nodes.The steady-state power history provided for the limiting transient clad strain case in Table 2 has 28 time steps. The axial power shapes corresponding to each of these burnup steps are given in Table 4. For the transient clad strain analysis,]a.c and since this is compatible with the FRAPCON 3.4 code capability, the shapes in Table 4 are defined for [ ac.Transient clad strain analyses are performed Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 1 0 A-8]". The magnitude of the local power increase is determined by the nuclear design analysis []Sc. For the Watts Bar Unit 2 analysis for TCD, the maximum transient clad strain occurred [ ]a,c. The transient power increase is modeled []a,c]a'c uncertainties that can result in increased transient local power peaking are accounted for in the clad strain analysis, as shown below.The transient axial power shapes for the best estimate transient, and for each of these uncertainty cases, are provided in Table 5.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 1 0 A-9 Table 3 Steady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal Pressure Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 1 0 A-10 Table 3, Continued Steady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal Pressure Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-11I Table 3, Continued Steady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal Pressure Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 1 0 A-1 2 Table 3, Continued Steady-State Axial Power Distributions by Burnup Step for Limiting Rod Internal Pressure Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 0 A-13 a,c Table 4 Steady-State Axial Power Distributions for Limiting Transient Clad Strain Analysis Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 1 0 A-14 Table 5 Clad Strain Analysis Transient Axial Power Distributions for Time Step 27 a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page LCN-WATTS-122 0 A-15 C. Fuel Rod Design Specifications and Manufacturing Tolerances

1. At a minimum, this should include those variables identified in the following table.Response: The requested table is provided as Table 6. In Watts Bar Unit 2, there are two fuel rod types: U0 2 and ZrB 2 IFBA. The design parameters for both rod types are provided in Table 6, and footnotes are used to identify characteristics that are unique to the IFBA fuel rod design. This includes the percent of the rod with ZrB 2 coated pellets] the IFBA coating thickness and B 1 0 loading, the backfill pressure, a"c. All of the other parameters provided in the table are common to both rod types, with the exception of the fast flux factor. This value is dependent on both the fuel rod loading and the power history modeled, and values are provided for the IFBA and U0 2 rods analyzed for rod internal pressure and for transient clad strain.The Westinghouse fuel pellet design includes some features which are not directly modeled in FRAPCON 3.4, based on the input description in Appendix A of Reference 2.This includes the pellet edge chamfer and the annular axial blanket pellets. Dimensions for these features are provided in Table 6 to enable them to be accounted for in the FRAPCON 3.4 comparison analyses.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 1 0 A-16 Table 6 FRAPCON 3.4 Input Parameters for Watts Bar Unit 2 Fuel Analysis]a,c axU 1 1 2 ZrB 2 IFBA rods only Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-17 Table 6 FRAPCON 3.4 Input Parameters for Watts Bar Unit 2 Fuel Analysis a,c 1 ZrB 2 IFBA Rods Only 2 ZIRLO is a trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved.Unauthorized use is strictly prohibited.

Other names may be trademarks of their respective owners.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 0 A-18 Table 6 FRAPCON 3.4 Input Parameters for Watts Bar Unit 2 Fuel Analysis a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-19 2. For the following inputs from the above table, please provide tolerance values.Response: The requested tolerance values are provided in Table 7. Drawing tolerances are given as requested, but it is noted that design analyses axc Table 7 Fuel Pellet and Cladding Tolerance Values a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 1 0 A-20 3. For the AOO overpower (Fz vs. time) used in the clad strain calculation:

i. Provide the input used (power vs. time)Response: The axial power distribution, in kW/ft, for the limiting Condition II transient clad strain calculation, is provided in response to Item 1.B.1 in Table 5. The transient is modeled]a,c. Table 5 provides the limiting Condition II transient power duty on a best estimate basis and also provides the impacts of several uncertainties on the transient power, as discussed in response to Item 1 .B.1 ii. Provide the predicted strain for both fuel types Response: The limiting transient clad strain results calculated for the U0 2 and for the ZrB 2 IFBA fuel rods occurred [ ]a,c of the power history provided in Table 2 and are: U0 2 fuel rod [ ]a,c ZrB 2 IFBA fuel rod [ ], 4. Provide the predicted power to melt limit (kwlft) vs. Burnup for both fuel types Response: Table 8 summarizes the predicted power to melt limit as a function of local burnup for both ZrB 2 IFBA and U0 2 fuel. These results are also illustrated in Figure 3.Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-21 Table 8 ZrB 2 IFBA and U0 2 Fuel Power to Melt as a Function of Local Burnup a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-22 Figure 3 Power to Melt Limit for Watts Bar Unit 2 ZrB 2 IFBA and U0 2 Fuel with TCD a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-1 22 0 A-23 5. Provide the following for the Rod Internal Pressure case for both fuel types: i. BOL Void W ii. EOL Hot VV iii. EOL RIP iv. EOL FGR (% release and moles of Gas)Response The requested PAD 4.0 TCD results from the rod internal pressure analysis are provided in Table 9.Table 9 Reference PAD 4.0 TCD Rod Internal Pressure Analysis Results a,c Core Engineering Word Version 15-1 Westinghouse Non-Proprietary Class 3 WESTINGHOUSE ELECTRIC COMPANY LLC Calculation Note Number Revision Page CN-WATTS-122 0 A-24 References

1. WBT-TVA-2598, "PIN Request- Support of NRC Audit of the WEC work on Thermal Conductivity Degradation.doc," March 7, 2014.2. NUREG/CR-7022, Volume 1, PNNL-19418, Volume 1, "FRAPCON 3.4: A Computer Code for the Calculation of Steady-State Thermal-Mechanical Behavior of Oxide Fuel Rods for High Burnup," March 2011.Core Engineering Word Version 15-1